The Dow company announced [Me2Si(Me4C5)NtBu]TiCl2 (Constrained-Geometry Catalyst, CGC) early 1990s (U.S. Pat. No. 5,064,802). The CGC has two excellent properties in a copolymerization reaction of ethylene with alpha-olefin as compared to existing known metallocene catalysts, which is summarized as follows: (1) Even at a high polymerization temperature, high activity is exhibited and a high molecular weight of a copolymer is produced, and (2) it is significantly excellent for copolymerization of alpha-olefin having high steric hindrance such as 1-hexene and 1-octene. Besides, at the time of polymerization reaction, as various properties of the CGC have been gradually known, efforts to synthesize a derivative thereof to be used as a polymerization catalyst have actively been conducted in academic and industrial fields.
As one approach among the efforts, synthesis of a metal compound into which various bridges instead of a silicone bridge and a nitrogen substituent are introduced and polymerization using the synthesized metal compound have been attempted. Representative metal compounds known so far are shown as follows (Chem. Rev. 2003, 103, 283).

In the compounds shown as above, phosphorus (1), ethylene or propylene (2), methylidene (3) and methylene (4) bridges instead of the silicone bridge of the CGC structure are introduced, respectively. However, when the above listed compounds are applied to polymerization of the ethylene or the copolymerization of ethylene with alpha-olefin, as compared to the CGC, excellent results are not exhibited in view of a polymerization activity, a copolymerization performance, or the like.
As other approaches, compounds having an oxido ligand instead of an amido ligand of the CGC have been synthesized in many times, and polymerization using the compounds also has partially attempted.
However, among these attempts, only a few catalysts are commercially available in practice. Most of copolymers of ethylene and alpha-olefin polymerized using transition metal compounds have a narrow molecular weight distribution as compared to a low density polyethylene (LPDE) obtained from existing high pressure process; however, in view of a polymer structure, the copolymers of ethylene and alpha-olefin polymerized using the transition metal compounds do not include a long chain branch; or include a relatively small amount of long chain branch. Recently, efforts to obtain polyolefin-based copolymers having a polymer structure including a long chain branch and having various properties have actively been conducted in academic and industrial fields, and development of novel catalysts and processes has still been demanded.